PLANKTON STUDIES ON LAKE MEND OTA. I. 
THE VERTICAL DISTRIBUTION OF THE PELAGIC 
CRUSTACEA DURING JULY, 1894. 
E. A. BIRGE, 
Professor of Zoology, University of Wisconsin, 
ASSISTED BY 
o. a. olson and n. p. harder. 
INTRODUCTION. 
The following paper is the result of the joint work of Mr; 
Mr. O. A. Olson and H. P. Harder, members of the class of 
1895 of the University of Wisconsin, done under my direction,, 
and with my aid, for graduating theses in the College of Letters^ 
and Science. The observations occupied about six weeks of the* 
summer of 1894. The first ten days, beginning about July 5,. 
1894, were spent in preliminary work, experimenting with the- 
dredge and with methods of counting. The last observations^ 
were made on th«! 4th of August, and the finishing of the- 
counting of specimens occupied about another week. Messrs... 
Harder and Olson did most of the dredging, taking the observa¬ 
tions, day and night, at regular intervals whenever the state of 
the weather permitted. The observations at 6 and 9 p. m. were 
ordinarily made by myself. The counting and the exceedingly 
wearisome computation of percentages and averages was also 
performed by them. In this latter work Mr. Olson was re¬ 
sponsible for Cyclops and D. pulicaria, while Mr. Harder did 
the computing for Diaptomus and D. hyalina. Each, however,, 
checked the work of the other, so that great accuracy has been 
obtained, both in counting and in computation. Mr. Harder 
was absent after the completion of the observations, while Mr. 
Olson has been in attendance at the University and has. 
done much work during the college year. 
The results of the investigation were written up and reported; 
